Phys 181b Problem Set 12 Solution

# Phys 181b Problem Set 12 Solution - 3. Let R be the rate of...

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3. Let R be the rate of photon emission (number of photons emitted per unit time) of the Sun and let E be the energy of a single photon. Then the power output of the Sun is given by P = RE . Now E = hf = hc / λ , where h is the Planck constant, f is the frequency of the light emitted, and λ is the wavelength. Thus P = Rhc / λ and R P hc == × ×⋅ × λ 550 39 10 6 63 10 2 998 10 10 10 26 34 8 45 nm W Js m /s photons/ s. b gc h c hc h . .. .

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4. We denote the diameter of the laser beam as d . The cross-sectional area of the beam is A = π d 2 /4. From the formula obtained in problem 3, the rate is given by () ( ) 3 2 2 34 8 3 21 2 4 633nm 5.0 10 W /4 6.63 10 J s 2.998 10 m/s 3.5 10 m photons 1.7 10 . ms RP A hc d −− × λ == π π× × ×
18. To find the longest possible wavelength λ max (corresponding to the lowest possible energy) of a photon which can produce a photoelectric effect in platinum, we set K max = 0 in Eq. 38-5 and use hf = hc / λ . Thus hc / λ max = Φ . We solve for λ max : λ max .

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## This note was uploaded on 07/18/2008 for the course PHYS 181 taught by Professor Stephenirons during the Spring '08 term at Yale.

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Phys 181b Problem Set 12 Solution - 3. Let R be the rate of...

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